A system and method for heating subterranean oil-rich coal using oil vapor phase transition

Abstract

The application discloses a system and method for heating underground oil-rich coal by adopting oil vapor phase change, and the system comprises underground coal seams, a heat injection well, a production well, a water vapor generating furnace, an oil vapor generating furnace and a fractional distillation furnace and the like. The application adopts oil vapor as a heat carrying medium, injects the oil vapor, and releases a large amount of heat energy through condensation phase change in the underground coal seams, so that the rapid heating of the coal seams is realized, and then the process of extracting oil and gas is realized. The method focuses on the phase change heat exchange method between the heat carrying medium and the coal seams, utilizes a large amount of latent heat released in the condensation process, strengthens the heat exchange, completes the fast and energy-saving process of extracting oil and gas, reduces the volume of the components in the system, is beneficial to large-scale and efficient development of oil-rich coal resources, and promotes the transformation of energy utilization to the high-quality goal of carbon neutrality.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a system and method for heating underground oil-rich coal using oil vapor phase change. Background Technology

[0002] Pyrolysis of oil-rich coal can yield abundant high-grade oil and gas resources. In-situ underground pyrolysis development technology for oil-rich coal allows for the targeted and prioritized extraction of nationally scarce oil and gas resources. Simultaneously, the remaining semi-coke can support the overlying strata, ensuring the integrity of the unconfined aquifer and maintaining ecological stability. However, traditional methods of heating underground coal seams via heat conduction and convection suffer from slow heating rates, long heating times, and high consumption of heating media, hindering efficient and energy-saving utilization in the in-situ development of oil-rich coal. Summary of the Invention

[0003] For the in-situ mining of rich oil-bearing coal, slow heat transfer rate is a major technical challenge restricting rapid and large-scale mining. Therefore, this invention employs a phase change process using oil vapor to release heat from the underground coal seam. This invention provides a system and method for heating underground rich oil-bearing coal using oil vapor phase change. Oils with different boiling points absorb heat energy at the surface to generate oil vapor, which then liquefies and releases heat within the underground coal seam. This utilizes the large amount of latent heat of vaporization released during oil vapor liquefaction, thereby achieving efficient heat transfer from external input to the coal seam and significantly reducing equipment size.

[0004] The present invention is achieved using the following technical solution:

[0005] A system for heating underground oil-rich coal using oil vapor phase change includes a steam generator, an oil vapor generator, a fractionation furnace, and injection wells and production wells drilled in the underground coal seam;

[0006] The steam generator is equipped with a heating fuel inlet, and the oil steam generator is equipped with a heating fuel inlet, an external medium oil inlet, and a circulating medium oil inlet. The outlets of the steam generator, the oil steam generator, and the nitrogen source are connected to the inlet of the injection well. The injection well and the production well are connected through coal seam fractures. The outlet of the production well is connected to the inlet of the fractionation furnace. The fractionation furnace is equipped with an oil and gas production outlet and a circulating medium oil outlet, and the circulating medium oil outlet of the fractionation furnace is connected to the circulating medium oil inlet of the oil steam generator.

[0007] A further improvement of the present invention is that a valve No. 1 is provided at the outlet of the steam generator.

[0008] A further improvement of the present invention is that a second valve is provided at the outlet of the oil vapor generator.

[0009] A method for heating underground oil-rich coal using oil vapor phase change, the method being based on the aforementioned system for heating underground oil-rich coal using oil vapor phase change, comprising:

[0010] First, before the injection begins, nitrogen is used to displace the air in the underground coal seam. Valve No. 2 is closed, and Valve No. 1 is opened. The oil vapor generator heats the low-boiling-point external medium oil using fuel, generating oil vapor. This oil vapor is injected into the coal seam fractures through the injection well. During injection, because the temperature of the underground coal seam is lower than the condensation point of the external medium oil vapor, the oil vapor condenses from a gaseous state to a liquid state, releasing a large amount of heat energy to the coal seam. Simultaneously, the liquid oil vapor flows slowly through the fractures. Next, a medium-boiling-point external medium oil is selected to generate oil vapor in the oil vapor generator, which is then condensed and released heat into the underground coal seam. This medium-boiling-point oil vapor condenses into liquid oil, while the low-boiling-point liquid oil in the coal seam fractures is reheated into a gaseous state and flows out from the production well. This process is repeated for different boiling points of external medium oil. The underground coal seam is heated in stages, and eventually, the boiling point of the high-boiling-point external medium oil reaches 450℃. At this point, valve number one is closed and valve number two is opened. The steam generator produces steam at a temperature of 600℃ by heating the fuel. This high-temperature steam is injected into the underground coal seam through the injection well. The high temperature causes the high-boiling-point external medium oil to turn back into a gaseous state and flow smoothly out of the production well. At the same time, the underground coal seam is continuously heated to an even higher temperature by the steam, and the oil and gas components in the coal seam are further released. Under the action of oil steam condensation heating and steam convection heating, the temperature of the underground coal seam continues to rise, thereby releasing oil and gas components from the production well into the fractionation furnace. The fractionation furnace fractionates oil and gas with different boiling points. Part of it forms oil and gas production, while the other part of the circulating medium oil enters the oil steam generator as a heat transfer medium to transfer heat energy to the underground coal seam.

[0011] A further improvement of the present invention is that the method uses oil vapor as the main heat injection medium.

[0012] A further improvement of the present invention is that a set proportion of nitrogen is mixed into the oil vapor as a protective gas to reduce the oxygen content mixed in.

[0013] A further improvement of this invention is that, during the staged heating process, the boiling point of the oil vapor is ensured to be higher than the temperature of the coal seam, so that heat transfer can proceed smoothly.

[0014] A further improvement of the present invention is that the boiling point of the external medium oil is below 150°C.

[0015] A further improvement of the present invention is that the high-boiling-point external medium oil is heavy oil or asphalt. This external medium oil has high viscosity and slow flow after condensation in the underground coal seam.

[0016] A further improvement of the present invention is that, in order to prevent air leakage from causing the injection of heating oil vapor and explosion, the air in the coal seam is first displaced by positive pressure nitrogen before the injection begins, and the positive pressure state of the injection medium is maintained throughout the injection process.

[0017] The present invention has at least the following beneficial technical effects:

[0018] (1) Using oil vapor as the heating medium, the heat released by the condensation of oil vapor is used to heat the oil-rich coal seam. The oil-rich coal seam heats up quickly and the coal seam heating time is significantly shortened.

[0019] (2) The latent heat of vaporization released during the condensation process of oil vapor is huge, which allows less working medium to fully heat the coal seam, reduces the amount of heating working medium used, and reduces the size of equipment in the development of oil-rich coal.

[0020] (3) Using oil vapor with different boiling points as the heating medium to perform segmented heating of underground coal seams, the oil vapor with low boiling point condenses in the underground coal seam, and then the oil vapor with high boiling point enters the underground coal seam to evaporate the low boiling point medium, thus avoiding the blockage of the crack channel by the heating medium.

[0021] (4) The coal tar distilled from oily coal is processed to separate oil products with different boiling points, which can then be recycled as a heat injection medium.

[0022] (5) Oil vapor and pyrolysis products are both hydrocarbons and have the property of similarity solubility. Pyrolysis products are easy to dissolve in them and be extracted together, and the subsequent separation is also easier. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a system for heating underground oil-rich coal using oil vapor phase change according to the present invention.

[0024] Explanation of reference numerals in the attached figures:

[0025] 1 is the underground coal seam, 2 is the injection well, 3 is the production well, 4 is the coal seam fracture, 5 is the steam generator, 6 is the oil steam generator, 7 is the fractionation furnace, 8 is the oil and gas production, 9 is the heating fuel, 10 is the external medium oil, 11 is the circulating medium oil, 12 is valve number one, 13 is valve number two, and 14 is nitrogen. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings:

[0027] join Figure 1 This invention provides a system for heating underground oil-rich coal using oil vapor phase change, comprising a steam generator 5, an oil vapor generator 6, a fractionation furnace 7, and a heat injection well 2 and a production well 3 located in an underground coal seam 1. The steam generator 5 is provided with a heating fuel inlet, and the oil vapor generator 6 is provided with a heating fuel inlet, an external medium oil inlet, and a circulating medium oil inlet. The outlets of the steam generator 5 and the oil vapor generator 6, as well as a nitrogen source, are connected to the inlet of the heat injection well 2. The heat injection well 2 and the production well 3 are connected through a coal seam fracture 4. The outlet of the production well 3 is connected to the inlet of the fractionation furnace 7. The fractionation furnace 7 is provided with an oil and gas production outlet and a circulating medium oil outlet, and the circulating medium oil outlet of the fractionation furnace 7 is connected to the circulating medium oil inlet of the oil vapor generator 6. A first valve 12 is provided at the outlet of the steam generator 5, and a second valve 13 is provided at the outlet of the oil vapor generator 6.

[0028] This invention provides a method for heating underground oil-rich coal using oil vapor phase change, comprising:

[0029] (1) Through the heating effect of fuel 9, oils with different boiling points are heated in the oil vapor generator 6 to heat the external medium oil 10, thereby generating oil vapor. Then, this oil vapor is injected into the underground coal seam 1 from the injection well 2. This oil vapor flows through the coal seam fracture 4 and condenses and releases heat in the underground coal seam 1. The released latent heat of vaporization will rapidly heat the underground coal seam 1. Low-boiling-point oil vapor is injected first, followed by higher-boiling-point medium oil injected in stages. Medium-boiling-point oil replaces the low-boiling-point oil remaining in the coal seam fracture, and high-boiling-point oil replaces the medium-boiling-point oil. When the temperature rises to 450℃, valve 13 is opened and valve 12 is closed. High-temperature steam generated in the steam generator 5 is injected into the underground coal seam 1, which makes the coal continue to heat up and at the same time replaces the high-boiling-point oil remaining in the coal seam fracture 4, thereby achieving efficient heating of the underground coal seam and full recovery and utilization of the medium oil.

[0030] (2) To prevent air leakage from causing the injection of heating oil vapor and subsequent explosion, before the injection begins, valve 12 is opened and valve 13 is closed. Positive pressure nitrogen gas 14 is used to displace the air in the coal seam, and the positive pressure of the injection medium is maintained throughout the injection process. In addition, a set proportion of nitrogen is mixed into the oil vapor as a protective gas to reduce the oxygen content mixed in.

[0031] (3) During the cascade heating process, it is necessary to ensure that the boiling point of the oil vapor is higher than the temperature of the coal seam so that the heat transfer can proceed smoothly.

[0032] (4) The products released by the thermal decomposition of oil-rich coal are released from the production well 3 and separated into oil products with different boiling points after being processed by the fractionation furnace 7. One part is used as oil and gas production 8, and the other part can be used as circulating medium oil 11, so there is no need to introduce other oil products as heating medium from the outside.

[0033] Combined with appendix Figure 1 The specific working process of this invention is as follows:

[0034] First, before the injection begins, nitrogen gas (14) is used to displace the air in the underground coal seam 1. Valve 13 (number two) is closed, and valve 12 (number one) is opened. The oil vapor generator (6) heats the lower-boiling-point (generally below 150°C) external medium oil (10) using fuel (9), generating oil vapor. This oil vapor is injected into the coal seam fractures (4) within the underground coal seam 1 through the injection well. During injection, because the temperature of the underground coal seam is lower than the condensation point of the external medium oil (10), the oil vapor condenses from a gaseous state to a liquid state, releasing a large amount of heat energy to the coal seam. Simultaneously, the liquid oil flows slowly within the fractures. Next, a medium-boiling-point external medium oil (10) is selected to generate oil vapor in the oil vapor generator (6), which is then condensed and released into the underground coal seam 1. This medium-boiling-point oil vapor condenses into liquid oil, while the lower-boiling-point liquid oil in the coal seam fractures (4) is reheated back into a gaseous state and flows out from the production well. Different boiling points of external medium oil 10 are selected sequentially to heat the underground coal seam 1 in stages. Ultimately, the boiling point of the external medium oil 10 is relatively high (approximately 500℃, generally heavy oil or asphalt). This portion of the external medium oil, after condensation in the underground coal seam 1, has a high viscosity and flows relatively slowly. At this point, valve 12 is closed and valve 13 is opened. The steam generator 5 generates steam at a temperature of 600℃ by heating fuel 9. This high-temperature steam is injected into the underground coal seam 1 through the injection well 2. Its high temperature allows the high-boiling-point external medium oil 11 to revert to a gaseous state and flow smoothly out of the production well. At the same time, the coal seam is continuously heated to an even higher temperature by the steam, and the oil and gas components in the coal seam are further released. Under the action of oil vapor condensation heating and water vapor convection heating, the temperature of the coal seam continues to rise, thereby releasing oil and gas components from the production well 3 into the fractionation furnace 7. The fractionation furnace 7 fractionates oil and gas with different boiling points, forming oil and gas production 8. Another part of the circulating medium oil 11 enters the oil vapor generator 6 as a heat transfer medium to transfer heat energy to the underground coal seam 1, thus eliminating the need for additional replenishment of external medium oil 11.

[0035] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A method for heating underground oil-rich coal using oil vapor phase change, characterized in that, This method is based on a system that uses oil vapor phase change to heat underground oil-rich coal. The system includes: a steam generator (5), an oil vapor generator (6), a fractionation furnace (7), and a heat injection well (2) and a production well (3) located in the underground coal seam (1). The steam generator (5) is equipped with a heating fuel inlet, and the oil vapor generator (6) is equipped with a heating fuel inlet, an external medium oil inlet, and a circulating medium oil inlet. The outlets of the steam generator (5), the oil vapor generator (6), and the nitrogen source are connected. The inlet of the injection well (2) is connected to the production well (3) through a coal seam fracture (4). The outlet of the production well (3) is connected to the inlet of the fractionation furnace (7). The fractionation furnace (7) is equipped with an oil and gas production outlet and a circulating medium oil outlet. The circulating medium oil outlet of the fractionation furnace (7) is connected to the circulating medium oil inlet of the oil vapor generator (6). A valve (12) is installed at the outlet of the steam generator (5). A valve (13) is installed at the outlet of the oil vapor generator (6). The method includes: First, before the injection begins, nitrogen (14) is used to displace the air in the underground coal seam (1), valve number 2 (13) is closed, and valve number 1 (12) is opened. The oil vapor generator (6) heats the low-boiling-point external medium oil (10) by heating fuel (9) to generate oil vapor. This oil vapor is injected into the coal seam fracture (4) in the underground coal seam (1) through the injection well (2). During the injection process, because the temperature of the underground coal seam is lower than the oil vapor condensation point of the external medium oil (10), the oil vapor condenses from a gaseous state to a liquid state. During this process, the coal seam... A large amount of heat energy was released. At the same time, the oil vapor turned into liquid and flowed slowly in the cracks. Then, the medium-boiling-point external medium oil (10) was selected to generate oil vapor in the oil vapor generator (6) and condense and release heat into the underground coal seam (1). This part of the medium-boiling-point oil vapor condensed into liquid oil. At the same time, the low-boiling-point liquid oil in the coal seam crack (4) was reheated into gas and flowed out from the production well (3). The underground coal seam (1) was heated in stages by selecting external medium oils (10) with different boiling points. Finally, the boiling point of the high-boiling-point external medium oil (10) reached 450°C. ℃; At this time, valve No. 1 (12) is closed and valve No. 2 (13) is opened; the steam generator (5) generates steam at a temperature of 600 ℃ by heating fuel (9), and injects this part of high-temperature steam into the underground coal seam (1) through the injection well (2). Its high temperature causes the high-boiling-point external medium oil (11) to turn into gas again and flow out smoothly from the production well (3). At the same time, the underground coal seam (1) is also continuously heated to a higher temperature by steam, and the oil and gas components in the coal seam are further released; the underground coal seam (1) is heated by the condensation of oil vapor and the convection heating of steam, and its temperature continues to rise, thereby releasing oil and gas components from the production well (3) into the fractionation furnace (7). The fractionation furnace (7) fractionates oil and gas with different boiling points. A part forms oil and gas production (8), and the other part of the circulating medium oil (11) enters the oil steam generator (6) as a heat transfer medium to transfer heat energy to the underground coal seam (1).

2. The method for heating underground oil-rich coal using oil vapor phase change according to claim 1, characterized in that, This method uses oil vapor as the heat injection medium.

3. A method for heating underground oil-rich coal using oil vapor phase change according to claim 2, characterized in that, A set proportion of nitrogen is mixed into the oil vapor as a protective gas to reduce the amount of oxygen mixed in.

4. A method for heating underground oil-rich coal using oil vapor phase change according to claim 2, characterized in that, During the cascade heating process, the boiling point of the oil vapor is kept higher than the temperature of the coal seam to ensure smooth heat transfer.

5. A method for heating underground oil-rich coal using oil vapor phase change according to claim 1, characterized in that, The boiling point of the low-boiling-point external medium oil (10) is below 150 °C.

6. A method for heating underground oil-rich coal using oil vapor phase change according to claim 1, characterized in that, The high-boiling-point external medium oil (10) is heavy oil or asphalt. This part of the external medium oil has high viscosity and slow flow after condensation in the underground coal seam (1).

7. A method for heating underground oil-rich coal using oil vapor phase change according to claim 1, characterized in that, To prevent air leakage from causing the injection of heating oil vapors and resulting in an explosion, positive pressure nitrogen is used to displace the air in the coal seam before the injection begins, and the positive pressure of the injection medium is maintained throughout the injection process.

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